The aims of this project are to understand the biology of papillomaviruses as related to laryngeal papillomatosis. The four projects focus on basic cell-virus interactions, a possible new therapy for the disease, and studies of the immune system in patients in an attempt to understand their susceptibility to the recurring papillomas. Progress has been made in each of these areas. In the following year Project 1 will work on improving the cell culture conditions for normal differentiation of laryngeal cells, and using microinjection of Human Papillomavirus (HPV) DNA to study viral stability in different cells. Project 2 will test different ways of applying the photodynamic therapy (ie topical vs injected drug, topical vs implanted laser light) and confirm that this therapy does not carry any detectable risk of malignant conversion. Project 4 will study the replication of different HPV types in various types of cells in vitro. Project 5 will continue to study the cell mediated immune system in the patients.